1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to saving power consumption by controlling listening periods in a wireless telecommunications device having a plurality of power-saving modes, and more particularly, to reducing power consumption by minimizing listening window periods when different powers saving classes are available in power-saving mode of a terminal device of a subscriber.
2. Description of the Related Art
In wireless telecommunications, power consumption of a terminal device is reduced by not constantly supplying power to the device.
When there is no traffic, an IEEE 802.16e wireless connection or telecommunications system using orthogonal frequency division multiple access (OFDMA) is put in sleep mode, i.e., power-saving mode, according to the IEEE 802.16e standard.
FIG. 1 illustrates mode switches according to traffic and power consumption according to the switches in a wireless telecommunications terminal device.
Different amounts of network traffic may exist in a broadband wireless connection system. A connection identifier(CID) corresponding to traffic may be allocated, and a power-saving class (PSC) is defined for each connection. In addition, a terminal device, while in sleep mode, wakes up regularly and receives information, from a base station, about whether there is traffic. Operations in sleep mode will now be described in detail.
First, a terminal device sends an MOB_SLP_REQ message to a base station to be put into sleep mode. Here, the terminal device sends desired PSC information, e.g., an initial sleeping window, a listening window, and a start frame number in units of a frame.
Second, the base station sends the terminal device an MOB_SLP_RSP message in response to the MOB_SLP_REQ message. Here, the terminal device sends the start time, i.e., the number of frames left until the terminal device is put in sleep mode, and PSC information approved in the base station.
Lastly, the terminal device put in sleep mode at a corresponding start frame number, wakes up after an initial sleeping window, and receives an MOB_TRF_IND message during a listening window period. If the MOB_TRF_IND message indicates no traffic, the terminal device stays in sleep mode, but if the MOB_TRF_IND indicates traffic, the sleep mode is terminated and the terminal device is put in normal mode.
Referring to FIG. 1, a packet is transmitted and received in normal mode 10, in which more power is consumed, while less power is consumed when the terminal device is in sleep mode 20. In listening mode 30, on the other hand, power consumption is as high as it is in normal mode 10 transceiving data. Hence, when the terminal device is frequently set in listening mode, more power is consumed. However, even if not frequently set in listening mode, efficiency is not high when data is transmitted and received.
FIG. 2 is a drawing illustrating sleep/listening periods of a terminal device having at least two power-saving modes when two power-saving modes are used. In the IEEE 802.16e standard, three types of PSCs are declared according to characteristics of different traffic. In a type 1 PSC, listening windows, related to the length of a listening mode, are constant in length, whereas sleeping windows, related to the length of a sleep mode, are multiplied by 2n. In a type 2 PSC, both the sleeping windows and the listening windows are constant in length. In a type 3 PSC, the sleep mode is on or off according to a constant trigger operation.
Therefore, the terminal device may have two or more PSCs corresponding to each CID. FIG. 2 illustrates use of power-saving modes by concurrently using PSCs defined as the type 1 PSC and the type 2 PSC in a terminal device. In the type 1 PSC, an initial sleeping window period is one frame and a listening window period is also one frame. The sleeping window period is 3 frames and the listening window is one frame in the type 2 PSC. The terminal device stays awake to perform normal transmitting and receiving operations during the listening window when two PSCs are used, receives an MOB_TRF_IND message from a base station, and indicates whether there is traffic to transmit to the corresponding terminal device during the sleeping window.
Sleep modes are used to minimize power consumption in a portable terminal device; however, when different PSCs are used, in a conventional method, it is likely that short sleeping window periods will be followed by a lot of listening window periods by an initial sleeping window, a listening window, and a start frame number. Hence, when there are two types of PSCs available in a single terminal device, it is essential to have a method of minimizing the listening window.